docs: def filter(pred: Callable, xs: Iterable):
      """
      Applied a predicate to a list returning a :py:class:`PromisedObject`
      containing the values satisfying the predicate.
  
      :param pred: predicate function.
      :param xs: iterable object.
      :returns: :py:class:`PromisedObject`
      """
      generator = (x for x in xs if pred(x))
  
      return gather(*generator)